1. Technical Field
The present invention generally relates to a method of recording information on a recording medium having at least one recording track, which recording track is divided into logic blocks which each have an individual logic address. The recording medium may be, for example, a magnetic or optical recording medium. The present invention typically and particularly though not exclusively relates to recording on an optical disc and will therefore be elucidated with reference to this example of use. However, it is emphasized that the invention is also applicable to other fields of use, such as for example tape recording.
2. Related Art
In general, the amount of information to be recorded in a recording session is greater than one block. The information to be recorded, also referred as xe2x80x9cfilexe2x80x9d, is then divided into successive data packets having the size of one block, and the successive data packets of a file are recorded in different blocks of the recording medium, which for the sake of simplicity is referred to hereinafter as xe2x80x9crecording discxe2x80x9d. For a rapid data transfer it is then desirable that the successive data packets are recorded in successive blocks. The recording process can then proceed virtually continuously. Likewise, during the subsequent reading (playback) of the information recorded on the disc the read process can proceed continuously.
In practice, a disc may exhibit defective blocks, i.e. blocks where a faultless recording of information is no longer possible or where any resulting small write errors can no longer be corrected during reading. Such a block is then no longer suited for recording. The only remedy is then to record the data packet that was to be stored in such a defective block in another block.
In a conventional manner the blocks are tested for defects by checking during a write operation whether recording has been effected correctly. Such a check, which is referred to as xe2x80x9cread-after-writexe2x80x9d check, is in principle carried out on a block-by-block basis, although it is also possible to record a plurality of blocks and subsequently check a plurality of blocks. Basically, a read-after-write test procedure implies that an information packet is stored in a read-after-write memory having the size of one block, which is read out after recording of the block just written, and that the information read from said block is compared with the information packet stored in the read-after-write memory. If these two information packets correspond the conclusion is drawn that recording has been successful and a following information packet may be recorded in a following recording block of the recording track. However, in the case of a difference between the two information packets it is inferred that recording has not been successful and the recording of the relevant information packet is repeated. A new recording attempt, also termed a xe2x80x9cretryxe2x80x9d, may be effected in the same block but if after a given number of retries the recording in this block still fails, this block is considered to be a defective block in which recording is not possible and the recording of the relevant information packet proceeds in another block. In this way it is achieved that the information is recorded in a reliable manner.
A recording method utilizing such a read-after-write test procedure and a possible new recording attempt in order to repair damaged information requires comparatively much time. Such a recording method is therefore less suitable for uses where an information stream with a high data rate is to be recorded. Such a use is, for example, a real-time recording of audio and/or video signals.
It is an object of the present invention to provide a recording method and recording apparatus which are more suitable for the recording of information streams with a high data rate, particularly real-time recording of audio and/or video signals.
The present invention more particularly aims at providing an apparatus of the aforementioned type which is suitable as a digital audio and/or video recorder.
It is known per se that a recording apparatus is adapted to first examine the quality of the recording blocks in a test cycle prior to the actual recording process. If defective blocks are detected the sequence numbers or addresses of these blocks are stored in a memory and, subsequently, this memory is addressed during the actual recording process and the defective blocks are skipped. However, testing is again effected with the aid of a read-after-write process and, as a result, the test cycle requires much time before the actual recording process can start.
In accordance with a first major aspect of the present invention the recording medium itself contains a list of addresses of defective blocks. This list is present in a file which should never be overwritten. For this purpose this file may be situated in a predetermined portion of a recording track but, alternatively, this file may have a predetermined name and the recording apparatus is adapted to use the file having this name exclusively for the recording of addresses of defective blocks.
In accordance with another major aspect of the present invention the recording apparatus is adapted to read said file prior to a recording session and to store the block addresses specified therein in an auxiliary memory and to read said auxiliary memory during the recording session and to skip the blocks whose addresses appear in this auxiliary memory during recording.
This prevents recording attempts being made for blocks which are already known as defective blocks. Thus, no time is lost with recording attempts which are doomed to fail.
It is known per se that during the read-out of information (playback) errors may occur, in view of which a read apparatus includes an error correction system, and error correction information for use in this error correction system is recorded during the recording of the data packet. Such an error correction system enables comparatively small errors to be corrected. These errors may have occurred during recording and may be present on the recording medium itself, or they may be produced during reading without an error being present on the recording medium. The extent to which such errors can be corrected depends on the error correction system used; since error correction systems are known per se and the present invention can be used in conjunction with known error correction systems, no detailed explanation of an error correction system will be given herein.
In accordance with a further major aspect of the present invention the quality of the data packets read from each block read during the read-out of the information (playback) is monitored. If a given data packet is found to exhibit incorrigible errors or if reading of a block fails completely, but preferably also if the number of corrigible errors appearing in one block is greater than a predetermined acceptance limit, the address of the relevant block is stored in a second auxiliary memory. After completion of the playback session the blocks whose addresses have been stored are tested. During such a test a standard read-after-write operation is carried out for these blocks in the course of the test process.
The test process for each block includes a step in which a restoration attempt is made. This block is then read one more time, the data packet thus read being presented to the error correction system. If the error correction system is capable of actually correcting the error the restored data is recorded in the relevant block instead of the information just read out, after which a standard read-after-write operation is performed for the restored data in order to ascertain whether recording has taken place in a satisfactory manner. Thus, the error is corrected actively, as a result of which less errors occur during a subsequent read-out and the delay in the data transmission owing to the need for error correction is smaller.
However, if the error correction system cannot correct the error in the information read, it is examined whether the error is merely a non-recurrent write error in an otherwise faultless block, or whether the recording block itself is defective. For this purpose, a predetermined data pattern or code word is recorded in the relevant block, after which a standard read-after-write operation is performed for said code word in order to check whether recording has been effected correctly. If this is the case, the block is apparently not defective; during a subsequent read cycle the code word is recognized as a xe2x80x9cdummyxe2x80x9d. Otherwise, the relevant block is definitively marked as being defective, for which purpose the address of this block is recorded in said file on the recording medium. As has been explained hereinbefore this prevents this block from being addressed during a subsequent recording session.
Furthermore, it is also possible to skip the restoration step and to include each block whose address has been noted during playing in the list of defective blocks as a standard procedure. As a result of this, the apparatus will be ready more rapidly at the end of a playback session but, on the other hand, a comparatively large number of blocks is labeled as being detective, which eventually results in an unnecessary reduction of the storage capacity of the recording medium.